Desalination of sea or brackish water by multi-stage flash evaporation

ABSTRACT

A flash desalination evaporator having a number of expansion chambers in series and discharge openings for flow of water between the chambers, the chambers, in which each chamber has a transverse dam, shaped in vertical section like half of a sine curve, sloping with its upper edge forward in the direction of flow, and standing from 5 cm. to 10 cm. higher than the upper side of the flow opening.

Aug. 15, 1972 ARBA ETAL 3,684,661

D- B DESALINATION OF SEA OR BRACKISH WATER BY MULTI-STAGE FLASH EVAPORATION Filed April 15, 1970 3 Sheets-Sheet 1 U) 2. .Q 0 U) C (D c C 8 c o c FL m N v N l N CONDENSER All. 15, 1972 BARBA ETAL ION UP SEA OR BHACKISH WATER BY 3,684,51 DESALINAT MULTI-STAGE FLASH EVAPORATION 3 Sheets-Sheet I Filed April 15, 1970 Aug. 15, 1972 D. BARBA EFAL 3,684,661

DESALINATION 0F SEA OR BRACKISH WATER BY MULTI'STAGE FLASH EVAPORATION Filed April 15, 1970 5 Sheets-Sheet 5 United States Patent Office 3,684,661 Patented Aug. 15, 1972 US. Cl. 202-173 1 Claim ABSTRACT OF THE DISCLOSURE A flash desalination evaporator having a number of expansion chambers in series and discharge openings for flow of water between the chambers, in which each chamber has a transverse dam, shaped in vertical section like half of a sine curve, sloping with its upper edge forward in the direction of flow, and standing from 5 cm. to cm. higher than the upper side of the flow opening.

This invention relates to a plant for the desalination of sea or other water and more particularly to flash evaporators in which the water is caused to flow through a number of expansion chambers arranged in series.

During the desalination process, these chambers are maintained at a pressure which decreases in the direction of flow of the saline solution in course of evaporation.

In such plant, the shape and proportions of the expansion chamber are known to be of great importance.

In particular, the conformation of the chamber floor, in determining the degree of turbulence in the saline solution, affects the rate of evaporation by allowing the more or less complete release of the water vapour, so that the evaporative efficiency of the particular chamber approximates more or less to unity.

One object of the present invention is therefore a special design for the expansion chambers in [dash evaporators, whereby greater evaporative elficiency is made possible.

The invention provides a flash desalination evaporator having a number of expansion chambers in series and discharge openings for flow of water between the chambers, in which each chamber has a transverse dam, shaped in vertical section like half of a sine curve, sloping with its upper edge forward in the direction of flow, and standing from 5 cm. to 10 cm. higher than the upper side of the flow opening.

The flash evaporator here proposed may consist essentially of a number of interlinked expansion chambers, each of which comprises an evaporation zone and two separate condensation zones, the passage of the saline solution from chamber to chamber taking place through shaped openings, while the chamber floor is provided with a darn, which, apart from determining the positioning of the opening, is shaped so as to facilitate the release of water vapour from the saline solution and thus to minimise pressure drops.

To be more precise, the evaporator with which the invention is concerned may comprise:

A continuous casing running horizontally, which consists of a flat bottom, two side walls at right angles to the bottom, and a flat top joined to the side walls;

Two vertical longitudinal bafiles running the full length of the casing and enclosing a central zone (evaporation zone) and two symmetrical side zones (condensation zones); these bailies, which connect the bottom of the casing to the top, contain a discontinuity in which filters are fitted horizontally to trap the droplets while allow ing the water vapour to pass from the evaporation zone to the condensation zones;

Two nests of tubes, consisting of a multiplicity of tubes extending the entire length of the casing and arranged symmetrically in the respective condensation zones;

A number of vertical transverse baflles running transversely to the casing so as to divide the interior into several chambers; the lower parts of these baffles contain rectangular openings, the width of which does not exceed that of the evaporation zone, to permit the flow of liquid from chamber to chamber; and

A dam fitted transversely in the evaporation zone of each chamber, greater in depth than the flow opening and shaped like one half of a sine curve.

It has been found that a dam of this shape, while reducing the pressure drop, affects the movement of the saline solution so as to produce sufiicient turbulence to promote the escape of the water vapour.

These and other features of the plant constituting the object of the invention will be made clearer by the following description and the accompanying drawings, in which:

FIG. 1 is a diagrammatic cross-sectional view of an expansion chamber;

FIG. 2 is a diagrammatic longitudinal sectional view of the chamber along the line 2-2 in FIG. 1; and

FIG. 3 is a mixed or composite diagrammatic longitudinal section of a three-chambered evaporator, the upper part showing the condensation zone and the lower part the evaporation zone.

In FIG. 1, the numeral 1 indicates the continuous casing, 2 the vertical baflles enclosing one central evaporation zone 7, and two side zones 8 for condensation. The filters for trapping the droplets are numbered 3, while 4 is the flow opening through which the saline solution passes.

Still with reference to FIG. 1, the nests of heat-exchanger tubes in the condensation zones are numbered 5 and collectors for the non-condensable components are numbered 6.

In FIG. 2, 4 is the flow opening and 9 is the projection for determining the flow conformation. The droplet filter 3 is shown, and also a dam 10. The latter is shaped like half a sine curve having positive slope and rises to a height of 1, so as to stand 5 cm. to 10 cm. above the upper edge of the admission opening.

FIG. 3 shows the evaporator in longitudinal section and brings out, in particular, details of one of the two nests of tubes 5, and entry 11 for the solution that is to be evaporated and an outlet 12 for the concentrated solution after evaporation.

For seawater desalination, the saline solution enters the chamber through the opening with the shaped shutter, which should preferably be of the drop type, to enable the opening to be varied according to the duty required of the plant.

The water vapour evolved passes into the central zone of the chamber, goes through the droplet filter and condenses on the nests of tubes, collecting at the bottom.

In addition to greater evaporative efliciency, the evaporator here proposed has the advantage of greatly improving the effectiveness of the filter separators, apparently due to a considerable reduction in the amount carried over in consequence of the particular path of the vapour, which results in entrained material being dropped when the vapour impinges on the top of the chamber.

It is therefore possible to reduce the thickness of the filters, thus reducing the pressure losses through them, while still obtaining a distillate of remarkable purity.

Finally, all these features make the evaporator covered by the invention a more compact, rapid and eflicient unit for the desalination of seawater.

What we claim is:

1. A flash evaporator having a plurality of expansion chambers connected in series, each expansion chamber being provided with a central evaporation zone and two of the skirt between each pair of successive baffles, separate lateral condensation zones, comprising; said level dam having a cross-sectional configuration a closed skirt extending longitudinally and horizontalin the form of a semi-sinusoidal curve having a posily, said closed skirt formed by a planar bottom, two sidewalls positioned orthogonal to said bottom, and a top consisting of a substantially horizontal fiat wall merging into said sidewalls;

tive slope as defined by a sine curve between 31r/2 and 51r/2, and exceeding the height of the opening in said transverse vertical battle by 5 to cm., said dam and projection being the sole liquid flow modifying structures in the evaporation zone,

two heat exchangers, each heat exchanger consisting of a plurality of tubes extending longitudinally along the length of the skirt, each heat exchanger symmetrically positioned in a separate condensation two vertical baflles positioned within said closed skirt and extending along the length of said skirt, said vertical baflles positioned symmetrically within said 10 skirt and defining the central evaporation zone and the two lateral fully equal and symmetrical condensation zones, said longitudinal vertical baflles being zone. provided with a horizontal discontinuous offset hous- References Cited ing droplets separating filters permitting flow of vapor from the evaporation zone to the condensation zones; UNITED STATES PATENTS a plurality of transverse vertical bafi les extending trans- 3,146,177 8/ 1964 Chalmers et al 202173 X versely of said skirt and sub-dividing the interiors of 3,197,387 7/1965 Lawrance 159 2 MS X both the evaporation zone and condensation zones 3,336,966 8/1 967 Goeldner 159 2 MS into a plurality of chambers, each of said transverse 3,342,697 9/1967 Hammond 202173 vertical bafiles having a rectangular outflow opening 3,372,096 3/1968 Tidball 202-173 formed in the bottom thereof lying in the evapora- 3,395,084 7/1968 Loebel et a1. 202-173 tion zone, a shelfiike projection formed on said 3,427,227 2/ 1969 Chamberlin, transverse vertical baffles at the top of the outflow 3,203,464 8/1965 Kingma 1592 MS X opening extending in the direction of flow through said flash evaporator, said projection forming an angle with the vertical bafile above the opening of less than and extending into said chamber a length greater than the height of said opening through said transverse vertical baflle;

a liquid level forming dam provided on the floor of each expansion chamber and positioned transversely NORMAN YUDKOFF, Primary Examiner J. SOFER, Assistant Examiner 0 US. Cl. X.R. 

